This invention relates to injection of pressurized materials through a manifold, such as injection molding of plastic melt in a hot runner system. More specifically, this invention relates to an improved injection molding hot runner system in which the rate of melt flow is controlled through the gate during an injection molding cycle.
U.S. Pat. No. 5,556,582 discloses a multi-gate single cavity system in which the rate of melt flow through the individual gates is controlled independently via a control system according to specific target process conditions. This system enables the weld line of the part (the section of the part in which the melt from one gate meets the melt from another gate) to be selectively located. It also enables the shape of the weld line to be altered to form a stronger bond.
The ""582 patent discloses controlling the rate of melt flow with a tapered valve pin at the gate to the mold cavity. It also discloses placing a pressure transducer inside the mold cavity. Placing the pressure transducer inside the mold cavity can result in the pressure transducer sensing pressure spikes which can occur when the valve pin is closed. A pressure spike sensed by the transducer can cause an unintended response from the control system, and result in a less precise control of the melt flow than desired.
The control system disclosed in the ""582 patent uses the variables of valve pin position and cavity pressure to determine what position the valve pin should be in. Thus, the algorithm performed by the control system in the ""582 patent utilizes two variables to control the rate of melt flow into the cavity.
An injection molding apparatus and method are provided in which the rate of material flow during an injection cycle is controlled. According to one preferred embodiment, an injection molding apparatus is provided that includes a manifold, at least one injection nozzle coupled to the manifold, an actuator, and a valve pin adapted to reciprocate through the manifold and the injection nozzle. The valve pin has a first end coupled to the actuator, a second end that closes the gate in a forward position, and a control surface intermediate said first and second ends for adjusting the rate of material flow during an injection cycle. Retracting the valve pin tends to decrease the rate of material flow during the injection cycle and displacing the valve pin toward the gate tends to increase the rate of material flow during the injection cycle.
According to another preferred embodiment, in an injection molding system having a manifold for injecting material into first and second mold cavities, respectively, and a controller for controlling the flow rate of material injected into the first and second mold cavities during an injection cycle according to first and second target profiles, respectively, wherein the first and second target profiles represent a desired value of first and second sensed conditions related to the flow rate of material injected into the first and second cavities during an injection cycle, respectively, a method is provided for creating at least the first target profile for the first mold cavity. The method includes the steps of shutting off a flow of material into the second cavity, and injecting material into the first cavity to determine what values of the first sensed condition produce an acceptable molded part in the first cavity, the values of the first sensed condition that produce an acceptable molded part constituting the first target profile.
According to another preferred embodiment, in an injection molding system having a manifold for injecting material into first and second mold cavities, respectively, and a controller for controlling the flow rate of material injected into the first and second mold cavities according to first and second target profiles, respectively, wherein each target profile represents a desired value of first and second sensed conditions related to the flow rate of material injected into the first and second cavities during an injection cycle, respectively, a method is provided for creating the first and second target profiles. The method includes the step of simultaneously injecting material into the first and second cavities; and based on the simultaneous injection of material, determining what values of the first sensed condition produce an acceptable molded part in the first mold cavity, the values of the first sensed condition that produce an acceptable molded part constituting the first target profile, and determining what values of the second sensed condition produce an acceptable molded part in the second mold cavity, the values of the second sensed condition that produce an acceptable molded part in the second mold cavity constituting the second target profile.
According to another preferred embodiment, in an injection molding system having a manifold for injecting material through first and second gates into one or more mold cavities, and a controller for controlling the flow rate of material injected through the first and second gates during an injection cycle according to first and second target profiles, respectively, wherein the first and second target profiles represent a desired value of first and second sensed conditions related to the flow rate of material injected through the first and second gates during an injection cycle, respectively, a method is provided for creating at least the first target profile, the method includes the steps of selecting a test first target profile to be executed by the controller, injecting material through the first gate into a cavity according to the test first target profile executed by the controller, and determining whether the material injected produces an acceptable molded part in the cavity.
According to another preferred embodiment, in an injection molding system having a manifold for injecting material through a first gate into a first mold cavity, and a controller for controlling the flow rate of material injected through the first gate during an injection cycle according to a first target pressure profile by comparing a target pressure to an actual pressure during the injection cycle, wherein the first target pressure profile represents a target value of the pressure exerted by the material injected through the first gate during the injection cycle, a method is provided for creating the first target pressure profile. The method includes the steps of selecting a value of a variable corresponding to target injection pressure of the injected material, selecting a value of a variable corresponding to target pack pressure of the injected material, and selecting a value of a variable corresponding to a duration of the injection cycle.
According to another preferred embodiment, in an injection molding system having a manifold for injecting material through a first gate into a first mold cavity, and a controller for controlling the flow rate of material injected through the first gate during an injection cycle according to a first target pressure profile by comparing a target pressure to an actual pressure exerted by the material, a method is provided for creating the first target pressure profile. The method includes selecting pressure values for a plurality of variables corresponding to target pressures at a corresponding plurality of times during the injection cycle, and forming the first target pressure profile according to the pressure values.
According to another preferred embodiment, an injection molding apparatus is provided that includes a manifold for directing material through first and second gates into one or more mold cavities, and a controller to independently control a flow rate of material injected into through the first and second gates during an injection cycle according to a first target profile associated with the material injected through the first gate and a second target profile associated with material injected through the second gate. The first target profile represents target values of a first sensed condition related to the flow rate of material injected through the first gate during the injection cycle and the second target profile represents target values of a second sensed condition related to the flow rate of material injected through the second gate during the injection cycle. The apparatus further includes a graphical user interface for displaying at least the first target profile.
According to another preferred embodiment, an injection molding apparatus is provided that includes a manifold to direct material to first and second gates into one or more mold cavities, the manifold including first and second wells associated with each gate, a first ram to force material from the first well through the first gate, a second ram to force material from the second well through the second gate, and a controller to independently control first and second rates at which the first and second rams force material through the first and second gates and into the one or more mold cavities during an injection cycle.
According to another preferred embodiment, an injection molding apparatus is provided that includes a manifold to direct material into a mold cavity, a valve pin adapted to reciprocate through the manifold toward and away from the mold cavity, wherein valve pin contacts material injected into the mold cavity, and a controller to control a flow rate of material injected into the first cavity during an injection cycle based on a force exerted on the valve pin by the material.
According to another preferred embodiment, in an injection molding system apparatus having a manifold, at least one injection nozzle coupled to the manifold, an actuator, and a valve pin adapted to reciprocate through the manifold and the injection nozzle, the valve pin having a first end coupled to the actuator, and a second end that closes the gate, a method is provided having the steps of prior to the beginning of an injection cycle, placing the valve pin in a rearward position, moving the valve pin forward from the rearward position at the beginning of the injection cycle toward the gate to an intermediate position in which material flow is permitted, and moving the valve pin further toward the gate from the intermediate position to close the gate at the end of the injection cycle.
According to another preferred embodiment, in an injection molding system having a manifold to direct material to first and second gates, the manifold including first and second wells associated with each gate, a method is provided including the steps of injecting material into each of the first and second wells, injecting material from the each of the first and second wells through each of the first and second gates, and independently controlling the rates at which the material is injected from the first and second wells.
According to another preferred embodiment, in an injection molding system having a manifold to direct material to first and second gates which lead to one or more mold cavities, the first and second gates having first and second valve pin associated therewith, a method is provided having the steps of injecting material into the manifold, determining a first force exerted by the material on the first valve pin, and a second force exerted by the material on the second valve pin, respectively, and independently controlling the rate at which the material is injected through each of the first and second gates into the one or more mold cavities based on the first and second forces, respectively.
According to another preferred embodiment, in an injection molding system having a manifold to direct material to first and second gates which lead to one or more mold cavities, a method is provided that includes the steps of injecting material into the manifold, controlling in the manifold a first rate at which material is injected through the first gate into the one or more mold cavities based on a first pressure sensed in the one or more cavities, and controlling in the manifold a second rate at which material is injected through the second gate into the one or more mold cavities based on a second pressure sensed in the one or more cavities.